A semiconductor device, such as a CMOS transistor, has a connection structure including a wiring layer and a substrate, or a wiring layer and another wiring layer. In detail, as shown in FIG. 17, a contact hole 20 is formed between the P/N impurity diffusion layer (diffusion layer) 10 of a Si substrate (Si wafer) and a first wire, and a via hole 30 is formed between the first wire and a second wire. The contact hole 20 and via hole 30 are filled with metal such as tungsten or copper, and are electrically connected to the Si substrate or a wiring layer. Recently, prior to the filling of metal, barrier layers, such as Ti/TiN laminate layers, are formed in the contact hole 20 and the via hole 30, and thus barrier layers 22 and 32 are formed.
Conventionally, for the formation of a Ti layer or a TiN layer, physical vapor deposition (PVD) was used. However, at the present time, when the refinement and high-integration of semiconductor devices are conducted, the aspect ratio (ratio of diameter to depth) of a contact hole or a via hole has greatly increased. Due thereto, chemical vapor deposition (CVD) having good step coverage has been frequently employed in the formation of a barrier layer.
However, in order to reduce the contact resistance of metal in the diffusion layer 10 and the contact hole 20, it is preferable to interpose, for example, an alloy layer 12, such as a TiSix film (titanium silicide film), between the barrier layer 22 and the diffusion layer 10, and to adjust the work functions of the interfaces between the barrier layer 22 and the diffusion layer 10, thus decreasing a Schottky barrier based on the difference between the work functions.
For example, plasma CVD may be used to form such a TiSix film. This technique is configured to use H2 gas as reducing gas while using TiCl4 gas as a raw gas, and to form a Ti film at a temperature of about 650° C. and form the alloy layer 12 in a self-aligning manner by reacting part of the Ti film with the Si substrate simultaneously with the formation of the Ti film.
In addition, a method of forming a film by dividing a Ti film having a predetermined thickness through a plurality of processes has been proposed. For example, the following Patent Document 1 discloses plasma sequential flow deposition (SFD) as such a division film forming method. According to this processing method, a Ti film is prevented from being peeling and coming off even if the film is formed at a low temperature of, for example, 450° C. or less, and, as a result, a Ti film having good film quality can be formed.
Patent Document 1: Japanese Patent Application Publication No. 2004-232080
However, a request for a decrease in the temperature of film formation has recently increased mainly for the purpose of the realization of high-speed in semiconductor devices. Due thereto, a target substrate is preferably maintained at a low temperature (for example, 450° C. or less) even in the case of the formation of the barrier layer of a contact hole. However, when a Ti film is formed at low temperature using conventional plasma CVD, there is a problem in that a large amount of Cl remains in the Ti film, thus increasing the resistance of the Ti film.
Accordingly, a high-quality Ti film in which an excessively small amount of Cl remains even at low temperature can be formed in accordance with the formation of a Ti film based on plasma SFD. However, a Ti film formed by executing the plasma SFD at a high temperature of, for example, 650° C. or more reacts with a Si substrate, thus being easily silicided; and, as a result, a good TiSix film can be formed. However, since a Ti film formed by executing plasma SFD at a low temperature of, for example, 450° C. or less cannot be easily silicided, it is difficult to form a good TiSix film.